The effects
on each person depend on the user's experience, as well as:
how strong the marijuana is (how much THC it has);
what the user expects to happen;
where (the place) the drug is used;
how it is taken; and
whether the user is drinking alcohol or using other drugs.

Some people feel nothing at all when they smoke
marijuana. Others may feel relaxed or high. Sometimes it makes users
feel thirsty and very hungry - an effect called "the munchies."
Some users suffer bad effects from marijuana.
They may suffer sudden feelings of anxiety and have paranoid thoughts.
This is more likely to happen when a more potent variety of marijuana
is used.

If someone is high on marijuana, he or she might
seem dizzy and have trouble walking;
seem silly and giggly for no reason;
have very red, bloodshot eyes; and
have a hard time remembering things that just happened.
When the early effects fade, over a few hours, the user can become
very sleepy.

The short-term side effects
of marijuana include:
problems with memory and learning;
distorted perception (sights, sounds, time, touch);
trouble with thinking and problem-solving;
loss of coordination; and
increased heart rate, anxiety.

These effects are even greater when other drugs
are mixed with the marijuana; and users do not always know what
drugs are given to them.

The long-term side effects
from findings show that regular use of marijuana or THC may play
a role in some kinds of cancer and in problems with the respiratory,
and immune systems.

Cancer
It's hard to know for sure whether regular marijuana use causes
cancer. But it is known that marijuana contains some of the same,
and sometimes even more, of the cancer-causing chemicals found in
tobacco smoke. Studies show that someone who smokes five joints
per week may be taking in as many cancer-causing chemicals as someone
who smokes a full pack of cigarettes every day.

Lungs and airways
People who smoke marijuana often develop the same kinds of breathing
problems that cigarette smokers have: coughing and wheezing. They
tend to have more chest colds than nonusers. They are also at greater
risk of getting lung infections like pneumonia.

Immune system
Animal studies have found that THC can damage the cells and tissues
in the body that help protect people from disease. When the immune
cells are weakened, you are more likely to get sick.

Source: U.S. Department of Health and Human Services
NIH Publication Number 98-4037